Electrolytic iron manufacture



rlllllllllL CELL ahpwto'cs I Ml Her C1 27 6. Erik anJ B yw i B. MILLERET AL ELECTROLYTIC IRON MANUFACTURE Filed Sept. 21, 1931 April 13',1937.

w v fi L Lrllii 23F llllll Ill" w g 2 ,Lu: 2 ".5 f K .1. UHHHI UPatented ear. it, rest ELECTROLYTIC IR'ON MANWA f Delaware ApplicationSeptember 21, 1931', Serial No. stress iscleims.

This invention relates to the manufacture of electrolytic iron,particularly in the form of pipes or tubes.

The production of electrolytic iron has been'a subject or investigationfor many years,,but up to the present time no commercial process hasbeen sumciently successful to establish and maintain itself as anindustry. In the few processes which have been tried on any substantialscale,

the high consumption oii electrical energy, the low I the use of highlyconcentrated or dilutesolutions.

by changes in temperature of the electrolyte, by the use of oxidizingagents and by variously modifying other steps and factors involved inthe process. Such changes while apparently improving theprocess in somerespects have not materially aided in reducing. the cost of production.

The primary object of the present invention is therefore to overcome thedifficulties previously encountered and produce electrolytic iron tubesor other forms by a profitable commercial operation.

A further object of the present invention is to provide a commercialprocess for the manufacture of electrolytic iron tubes or sheets, bywhich a consistent smooth deposit of iron may be obtained in aneconomical manner.

A further object of the invention is the production of electrolytic ironsheets or tubes having a thickness suitable for present and futurecommerlcal uses. tubes or sheets made by previously triedprocesses isonly about 0.2 inch, while usually they were only 0.1 inch in thickness.Tubes of such thickness would not fulfill the requirements of modernboiler or oil still practice, or be suitable for high pressure gas andoil pipe lines. By the process of the present invention heavy walledtubes of any desired thickness may be made.

A further object of the invention is to provide a process'whereby oresmay be exploited where their content of phosphorus or of sulfur or bothmakes it impractical to use them in present ferrous metal productionprocesses. Experiments have shown that an anode having a relatively highcontent of phosphorus orsulfur, or both, has no efiect on the cellvoltage, and that such an anode gives a cathode deposit well within thecommercial limits for these substances.

The greatest known thickness for A still further object oi! theinvention is to provide a process for making electrolytic iron in whichvarious important factors are so controlled that iron tubes may beproduced on a commercial scale at a cost comparable with that forproducing steel tubes.

Another object of the invention is'the provision of a cell for theelectro-deposition of iron which includes a specially controlled acidelectrolyte and an anode having special properties.

With these and other objects in view the process of the presentinvention for the manufacture of electrolytic iron tubes or sheetscomprises one in'which the anode composition, the electrolytecomposition, temperature and acidity, the circulation of theelectrolyte, the spacing of the electrodes and other factors areaccurately controlled.

Further objects and advantages of the process will be apparent to thoseskilled in the art from the follewing detailed description taken incon.- nection with the accompanying drawing, in

which:---

Fig. l is a not showing of apmratus suitable for carrying out theprocess of the inventiom' Fig. 2 is alongitudinal view partly invertical section of one of the cells shown in Fig. 1;

Fig. 3 is a cross-section taken on the line 3-3 of Fig. 2, and.

Fig. 4 is a cross-section of the cell shown in Fig. 2 taken on the linet-t.

Referring to Fig. 1 of the drawing, the general features of the processwill be described in connection with the elements of the apparatusshown. In accordance with the present invention the iron to be depositedelectrolytically as tubes or sheets, is deposited from an acid solutionof ferrous chloride also containing sodium chloride solution,hydrochloric acid and sodium fluoride are introduced into a sump 2, fromwhich the solution mixture is withdrawn through a pipe 6 and passedby apump 8, pipe l0 and valved pipes it into a plurality of heating andstorage tanks it, it and it. (Any suitable numbermay be used.) In thesetanks the solution is heated to a suitable temperature by means ofdirectsteam introduced from a steam main 20 through submerged tubes 22 mountedin each tank. The solution in tanks it, it and it may also beheatedelectrically .or by steam coils 2t which may be connected through valvedpipes with the steam main 20. They storage tanks are also used assettling chambers for the removal of any suspended solid matter whichmay be presfluoride. In starting the process the ferrous eat in theelectrolyte. Such deposits as maysettie out in the tanks are withdrawnthrough valved drain pipes 26.

In carryingout the process electrolyte is usu- 5 ally supplied to onlytwo (or less than all) of the tanks at any one time, and the heatedelectrolyte is continuously withdrawn from these tanks through valveddischarge lines 28 and conducted by means of conduit 30 to a series ofcells 32, 34, etc. The electrolyte is introduced into each cell from theline 30 through a valved connection 36. While electrolyte iscontinuously introduced into each cell it is also continuously withdrawntherefrom through drain pipes 38 into a pipe 40 which leads to the sump2. During the operation of the process the electrolyte is circulatedat'a very rapid rate through the cells and back to the heating tanks inorder to prevent any sediment settling out in the cells and to maintainthe temperature and composition of the electrolyte in the cellssubstantially constant.

Any convenient number of cells may be used in connection with the linesand 40, only two being shown in Fig. 1 for purpose of illustration.

A more detailed showing of the cells 32, 34, etc.,.is given in Fig. 2 toFig. 4, from which it will be seen that the electrolyte is introduced atthe bottom and near the middle of each cell and withdrawn from both endsthereof. comprises an anode composed of a pair of preferablysemicylindrical cast iron pieces 42 suitably supported and insulatedfrom the remainder of r the cell as shown in the drawing. Within thesesemicylindrical anode elements is mounted a rotatable cathode 44,supported by blocks 45 outside the cell casing proper. The cathode maybe rotated at any suitable speed by means of a motor 48.

The cell casing is divided into at least three compartments by means ofpartitions 50, through which the cathode extends. The cathode may beprovided with deflector rings 52 adapted to prevent electrolyte whichflows along the cathode through the partitions 50, from flowing outsidethe cell casing. The end compartments outside partitions serve ascollecting basis for the electrolyte, which is discharged through pipes38. As shown in Fig. 3 the partitions 50 may be provided with overflownotches 54 to accommodate electrolyte in excess of that which flowsthrough the relatively small space between the cathode 44 and thepartitions 50. (Due to the relatively large amount of electrolytecirculated through the cells there may be a greater amount introducedthan would flow through the space around the cathode.)

Electricity may beconducted to the anodes in any suitable manner, forexample, by connections made to the anode supports as indicated in thedrawing and from any suitable source not shown. Likewise current may beconducted to the cathode through, brushes 56 or by any other suitablemeans.

In order to improve the iron deposit on the cathode the deposit is-wipedduring the rotation Each cell ously tried processes was largely due tothe necessary use of high cell voltage and relatively low currentdensity. One process for example used a voltage of 5 in order to obtaina current density of 60 amps. per square foot. In this connection it hasbeen discovered that an ironanode substantially free from carbon,silicon and manganese gives a much lower cell voltage than other iron.Furthermore, the presence of sulfur'and phosphorus in the iron has noadverse eflect'on the cell. The iron for the process therefore maycontain such quantities of sulfur and phosphorus as to be entirelyunsuited for the manufacture of steel.

In preparing the anode pieces for the cells, a blast furnace iron whichmay be high in phosphorus, is subjected to a modified Bessemer treatmentin that the iron is thoroughly blown with air to remove any carbon,silicon and manganese present. Then instead of recarburizing the iron asin the usual Bessemer process the iron is drawn at the end of the airblow and cast into anode pieces in substantially the form shown in Fig.4. The cathode may comprise an ordinary steel tube having suitablemounting flanges substantially as shown in Fig. 2.

In starting up the apparatus a substantially clean solution of thedesired composition is made up preferably in the sump 2 and then pumpedinto tanks l4, l6 and I8. The preferred solution I grams per liter ofsodium fluoride which prob- The solution is made ably acts as a butler.acid by the addition of hydrochloric, hydrofluoric or other acid untilthe solution has a pH value of from about 4 to 6, for example 5. The pHvalue of the electrolyte may be readily determined as follows: Take a 10c. 0. sample, dilute it with 40 c. c. of water and filter. To 10 c. c.of the filtrate add three drops of methyl orange; to a second 10 c. 0.add 3 drops of methyl red. The methyl orange-tinted solution should beyellow, and the methyl red-tinted solution should be red to show a pH ofabout 5. This simple test is based on the fact that the neutral point ofmethyl orange is 4.2, while that for methyl red is 5.8. The dilution ofthe sample has substantially no effect on its pH because the solution iswell buffered.

The use of a ferrous iron electrolyte of the particular concentrationrange referred to is preferred because the experimental work on thisprocess has demonstrated that such a. concentration range gives alowercell resistance than either a more dilute or a more concentratedsolution. M

After the electrolyte has been made up and all tanks (l4, l6 and I8)filled, the electrolyte in tanks l4 and I6 is heated to a temperature offrom 65 to 106 C. (preferably to 0.). Circulation of the electrolyte isthen started from tanks l4 and I6 through lines 28 and 30 to cells 32,34 etc., as previously referred to; the cells being cut into the circuitone at a time. During this operation (and before if desired to check itsproperties) a portion of the electrolyte is bypassed through a valvedpipe 62 into a control box (or room) 64 then into sump 2 through a pipe68. The temperature acidity and concentration of the electrolytepassing. through the control box 64 may be determined by well-knowninstruments or tests, the results of which may be used as a basis forany necessary additions of acid or of the salts referred to, or. for thecorrection of any other property of thesolution. Changes in temperature,concentration, gravity and acidity "may be adjusted automatically fromthe control box by the use of well-known devices for this purpose. Whilesatisfactory iron deposits may be obtained by maintaining thetemperature of the electrolyte in the range of from 65 to 106 C. it hasbeen found that at temperatures of from 90 to 95 C. the voltage is lowerfor a given current density than that required for the samecurrentdensity at lower temperature. Atthe preferred temperature range(90 to 95 C.) the loss from evaporation of the solution is much lessthan at higher temperatures.

The electrolyte is circulated at a relatively high rate from thetanksthrough the cells for the purpose of maintaining the temperature and tokeep the electrolyte in a high state of agitation in the cells. Therotation of the cathode is maintained at a'peripheral speed of about 100meters per minute. This rotation also serves to agitate the electrolyteand to assure a substantially con- I stant supply of fresh hotelectrolyte in the space between the cathode nd anode. The anode pieces42 are spaced sot at all parts of the-cathode are equally distanttherefrom, and so that the space between the cathode and anode pieces isas short as possible. With the method of control used in accordance withthe present invention it is possible to use a. spacing between theelectrodes as small as one half inch or less. The smaller the spacingthe lower the resistance in the electrolyte and the lower the cellvoltage becomes. As the anode material is removed by electrolysis thethickness of the iron deposited on the cathode increases, but if desiredany necessary adjustment in the spacing between the electrodes may bemade during a run by moving the i0 anode pieces closer to or away fromthe cathode.

Under the conditions given above it has been found possible to maintaina current density of 100 amps. 'or higher per square foot and at thesame time not have a. cell voltage greater than one. The importance ofthis relationship is apparent when it is realized. that the higher thecurrent density the-more rapid therate of iron deposition, and the lowerthe voltage the more economical the process. In one specific run undersubstantially the conditions-herein described the cell voltage-was 0.84.

. As the operation of the process proceeds the cells 32, it, etc., maybe alternately cut out of the system, the cathode removed and thedeposited iron stripped therefrom in any suitable manner. For examplethe deposited iron maybe removed by. heating and rolling, a method commonly referred to in the art. It will be seen therefore with a number ofcells connected to so the lines 30' and Ml that cells will be constantlycut in and out of the circuit.

After about eight hours operation with tanks it and it, tank is which isfilled with electrolyte will be heated and cut intothe system, whiletank it will be out out of system and the electrolyte therein allowed tosettle. After the electrolyte in tank it has been allowed to stand andsettle for a suitable period of time any sludge settled out therein maybe withdrawn through the valved pipefifi to any suitable storage. Therelatively clear stratifled solution may be drawn ofi and conducted intothe circuit or other storage if the tank needs cleaning. After the tankIt has been cleaned, it is then ready to he refilled, 75 heated and usedin place oitank it. Instead of using the settling it, it and i8 othersuitable means may be employed for heating the electrolyte and a filtermay be used for removing any suspended material.

The salt (sodium fluoride) used in connection with the process of thepresent invention is very eifective for maintaining the proper pH range.

even though relatively large amounts oi acid are added at a time. Ifsodium fluoride is not available other fluorides soluble in theelectrolyte may be used, for example potassium fluoride or hydrofluoricacid. g I It is the object of the present invention to operate theprocess under such conditions that the electrolyte will be protected asfar as possible from oxidation, and to avoid the presence of organicimpurities (or organic addition agents) in presence of carbon,phosphorus or sulfur.

Having described the invention in its preferred 1 form what is claimedas new is:

1. In the process of depositing iron electrolytically on a rotarycathode substantially surrounded by an iron anode submerged in a ferrouschloride electrolyte containing sodium fluoride,

the improvement which comprises mechanically rubbing the cathode as itrotates, supplying elecor about 10b amperes per square ioot'oi" cathodesurface at a voltage of about one, maintain 'ing the concentration offerrous chloride in the electrolyte at from 350 to too grams per literoi ferrous chloride tetdrate and that of sodium fluoride at from 10 to20 grams per liter,

eating the electrolyte to a temperature or from 65 to 166 (2., andmainng the pHvalue of the electrolyte between about 4 and 6.

2. The process'deflned in claim 1 in which the cathode is rotated at a,peripheral speed of about 100 meters per minute.

3. In the process of manufacturing electrolytic iron tubes in which ironis deposited on -a. rotating cathode substantially surrounded by a castiron anode substantially free of carbon submerged in a ferrous chlorideelectrolyte contained in a cell chamber, the improvement which comprisescontinuously circulating the electrolyte from said chamber through aheating zone in which the electrolyte is heated to a temperature of fromto C. and then back to the said chamber, maintaining all parts of thecathode substantially equidistant from the anode,

said electrolyte containing-from ill to 20 grams per liter of a solublefluoride, and controlling the concentration of the electrolyte tomaintain it slightly acid and'the content bi ferrous chloridetetrahydrate between 350 and sec liter. I

i. The process defined in claim 3 in which said cathode is rotated at aperipheral speed or about wiimeters per minute, and mechanically wipingsaid cathode during said rotation. I

5. The process defined in claim 3 in which the acidity. of theelectrolyte is maintained at a pH value between 4 and 6 by the periodicaddition of hydrochloric acid thereto.

grams per 'tricity to the electrodes at a current density electrolyticiron/comprising from 350 to 450 grams per liter of ferrous chloridetetrahydrate, 10 to 20 grams per liter of sodium fluoride, saidelectrolyte having a pH value of from 4 to 6 and being substantiallyfree of organic constituents. "I. The process ofelectrolyticallyconverting a high sulfur, high phosphoruscast iron intoa low sulfur, low phosphorus, iron. which com- 10 prises using an ironof such high sulfur and phosphorus content but substantially free ofcarbon silicon and manganese as anode material in an electrolytic cellin which the electrolyte is slightly acid, contains from 350 to 450grams per liter of ferrous chloride tetrahydrate and from 10 to gramsper liter of a soluble fluoride, and maintaining the temperature of saidelectrolyte between 65 and 106 C.

8. The process of electrochemically converting 20 impure ferrous metalscontaining phosphorus or sulphur into the substantially pure metal,which comprises subjecting such an impure metal substantially free ofcarbon, silicon and manganese as an anode in an electrolytic cell to theaction of an electric current and-an acid electrolyte maintained at atemperature between 65 and 106 C., depositing the substantially puremetal on a cathode in said cell, and maintainingthe hydrogen ionconcentration insaid electrolyte such that the electrolyte has a pHvalue of from 4 to 6 inclusive.

9. In the process of depositing iron electrolytically on a rotarycathode mounted between iron anode elements submerged in an electrolytecontained in a cell chamber, the improvement which comprises supplyingelectricity to the electrodes at a current density of approximately 100amperes per square foot and at a voltage of about one, maintaining inthe electrolyte a concentration of ferrous chloride tetrahydrate of,from 350 to 450 grams per liter and maintaining the electrolyte at atemperature of from 65 to 106 0., and sufllciently acid to give a pHreading of .from 4 to 6.

10. In the process of refining iron in which cast iron is used as anodematerial in an electrolytic cell for making electrolytic iron, theimprovement which comprises electroplating the cast iron anode materialon to a cathode 50 mounted in an electrolyte in said electrolytic cell,said anode material comprising cast iron which has been air-blown whilein a molten state until it is substantially free of carbon andthereafter cast into the desired anode shape, and said electrolytecomprising an acid ferrous iron solution containing a small proportionof a soluble fluoride buffer agent, and maintaining the can pH value ofthe electrolyte between about 4 and 6.

' 11. The process of electrolytically depositing a firm smooth coat ofiron on a cathode mounted in a body of an acidic ferrous electrolyte,which comprises passing an electric current having a voltage of aboutone at a current density of approximately.100 amperes per square foot ofcathode surface between said cathode and a cast iron anode mounted insaid body of electrolyte closely adjacent said cathode, said anodecomprising cast iron substantially free of carbon silicon and manganese,and maintaining a small proportion of a soluble fluoride bufler agent insaid electrolyte to control the pH value thereof.

12. A process for producing electrolytic iron, which comprisesdepositing iron on a cathode mounted in an acid ferrous chlorideelectrolyte maintained at a temperature of from 65 to 106 C. andcontaining a soluble fluoride in sufflcient proportion to act as aninorganic bufler agent for maintaining the acidity-of said electrolyteat from 4 to 6 pH value.

13. In the process of manufacturing electrolytic iron tubes in which theiron is deposited on a rotating cathode substantially'surrounded by acast iron anode substantially free of carbon and submerged in a slightlyacid ferrous chloride electrolyte contained in a cell chamber, theimprovement which comprises continuously circulating the electrolytefrom said chamber through a heating zone in which the electrolyte isheated to a temperature of from 65 to 106 C.

and then back to said chamber, maintaining all parts of the cathodesubstantially equidistant from the anode, controlling the concentrationof theelectrolyte'to maintain the ferrous chloride content thereofequivalent to from 350 to 450 grams per liter of ferrous chloridetetrahydrate, said electrolyte also containing from 10 to 20 grams perliter of a soluble fluoride.

14. An electrolyte for use in the manufacture of electrolytic iron,comprising an acid ferrous chloride solution containing a relativelysmall proportion of a soluble fluoride compound but in suflicientproportion to act as a builer for the electrolyte for maintaining it ata pH value of from 4 to 6.

15. A process for producing electrolytic iron, which comprisesdepositing iron on a cathode mounted in an acid ferrous electrolytemaintained at a suitable temperature for electrolysis, said electrolytecontaining suificient fluoride in solution to act as a buffer agent toaid in controlling the pH value of the electrolyte, adding acid to theelectrolyte during the electrolysis, and maintaining the pH value of theelectrolyte at from 4 to 6 during the electrolysis.

COLIN G. BENJAMIN MILLER.

